Circular knitting machines are generally considered a high precision type of knitting machine. Some types of conventional circular knitting machines have a needle cylinder which includes a cylinder base. The cylinder base is conventionally seated in a generally L-shaped bed and is supported in a rotatable manner by a bearing assembly that is positioned between the cylinder base and the L-shaped bed. The bearing assembly conventionally includes pairs of annular wire tracks and a plurality of ball bearings mounted between the pairs of wire tracks.
When this type of circular knitting machine is in operation, the needle cylinder increases in temperature particularly because the knitting tools which are guided in the needle cylinder perform rapid upward and downward movements. As the temperature in the needle cylinder increases, the heat formed therein is transferred from the needle cylinder to the cylinder base causing thermal expansion in and around the cylinder base. When the machine is stopped, however, the ambient atmosphere often cools the cylinder base. A distortion occurs which is caused by these temperature changes, i.e., temperature differential. This distortion substantially affects the machine's accuracy.
In one attempt to solve this problem in this type of circular knitting machine, as described in U.S. Pat. No. 4,489,573 by Engelfried et al. titled "Circular Knitting Machine," the circular knitting machine has an elastic support flange that moves the position of one of the circular wire tracks of a pair thereof responsive to pressure fluctuation (i.e., caused by the thermal expansion of the cylinder base) between the circular wire track and ball bearings. Another non-elastic support flange of the other corresponding circular wire track is anchored in such a way as to cooperate with the elastic support flange. The spacing between the wire tracks of the pair is increased and the wire tracks slide outwardly on the ball bearings. The thermal expansion of the cylinder base is thus compensated.
In the above prior art type of circular knitting machine, however, a preload or pretension is applied to the bearing assembly in order to maintain the machine accuracy. This results in an increased machine torque and, hence, an excessive load to the bearing assembly. This excessive load may cause damage to the bearing assembly thereby inhibiting the operational performance of the circular knitting machine. Moreover, the elastic support flange for holding one of the circular wire tracks also must be thin enough to obtain elasticity; this tends to result in machining distortion which also makes it difficult to obtain a high level of accuracy.